- List is immutable, 底层实现用的数据结构上linked list. head 是第一个元素，tail是其余元素
last是最后一个元素， init是除最后一个元素之外的元素
2. 插入排序算法
package chapter16
object TestList extends App{
def isort(x: List[Int]): List[Int] =
if (x.isEmpty) x
else insert(x.head, isort(x.tail))
def insert(x: Int, xs: List[Int]): List[Int] = {
if (xs.isEmpty || x <= xs.head) x :: xs
else xs.head :: insert(x, xs.tail)
}
val list0 = List(4,5,3,6,1,7,0)
println(isort(list0))
}
3. 使用pattern matching改进代码
package chapter16
object TestList extends App{
def isort(xs: List[Int]): List[Int] = xs match {
case List() => xs
case x::xs1 => insert(x, isort(xs1))
}
def insert(x: Int, xs: List[Int]): List[Int] = xs match {
case List() => x::xs
case y::ys => if (x <= y) x :: xs else y::insert(x, ys)
}
val list0 = List(4,5,3,6,1,7,0)
println(isort(list0))
}
4. 一阶方法
This section explains most first-order methods defined in the List class. A method is first-order if it does not take any functions as arguments.
不以函数为参数的方法称为一阶方法
5. 拼接实现reverse方法
def reverse(xs: List[Int]): List[Int] = xs match {
case List() => xs
case y::ys => reverse(ys):::List(y)
}
val list0 = List(4,5,3,6,1,7,0)
println(reverse(list0)) //List(0, 7, 1, 6, 3, 5, 4)
6.扁平化List
The flatten method takes a list of lists and flattens it out to a single list
7.drop 去掉前 n个， take 取前 n个
8.map 相当于R语言中的lapply
9.flatmap 如果 f返回的是list,则把所有的返回值拼接在一起返回
时间： 2024-08-06 20:13:26